Mean Ultimate Load Research Articles

Cyclic Load Testing and Ultimate Failure Strength of Suture Anchors in the Acetabular Rim

To determine the resistance to cyclic stress and load-to-failure strength of several suture anchors suitable for hip arthroscopy. Ten polyetheretherketone (PEEK) PushLock, PEEK SutureTak, and Bio-SutureTak anchors (Arthrex, Naples, FL); Lupine Loop BR anchors (DePuy Mitek, Norwood, MA); Bio-Mini Revo anchors (ConMed Linvatec, Largo, FL); and BioRaptor 2.9 AB anchors (Smith & Nephew, Andover, MA) were inserted in rotation into different locations on the rim of 4 matched pairs of potted acetabula clamped to the base of a servohydraulic testing machine. The anchors' sutures were cyclically pulled in line with the insertion angle. Displacement at 100 and 500 cycles, yield load, ultimate failure load, and failure mode were recorded. Statistical analysis was performed. Most of the displacement observed during cyclic loading occurred in the first 100 cycles, except for the BioRaptor 2.9 AB, which showed twice as much displacement at 500 cycles as at 100 cycles. The Lupine Loop BR cyclic displacement was greater than that of the PEEK PushLock (at 100 cycles also), Bio-SutureTak, and PEEK SutureTak at 500 cycles (P < .05). The BioRaptor 2.9 AB cyclic displacement was significantly greater at 100 and 500 cycles than that of the PEEK PushLock and Bio-SutureTak (P < .05). The mean ultimate failure loads for these anchors ranged from 154 N (PEEK SutureTak) to 255 N (Bio-Mini Revo) and was statistically equivalent (P = .139). Correlation analysis showed no significant associations between anchor stiffness, cyclic load displacement, or failure load. Anchors with specific indications for hip arthroscopy showed very little displacement and had consistent failure loads under cyclic conditions in the acetabular rim. All hip anchors except the BioRaptor 2.9 AB showed less than 2.0 mm of displacement after 500 cycles. Biomechanical testing of suture anchors designated for hip arthroscopy should be performed in the acetabular rim before their use. Suture anchors used for shoulder arthroscopy may not perform as well in the hip.

Biomechanical Comparison of a Modified Weaver-Dunn and a Free-Tissue Graft Reconstruction of the Acromioclavicular Joint Complex

Background: Most surgical reconstructions of the separated acromioclavicular joint do not address the injured ligaments and capsule of the acromioclavicular joint. Purpose: This study was undertaken to compare the biomechanical characteristics of a modified Weaver-Dunn reconstruction and an intramedullary acromioclavicular joint reconstruction that uses a free-tissue graft for reconstruction of both the coracoclavicular and acromioclavicular ligaments. Study Design: Controlled laboratory study. Methods: Each pair of 6 matched pairs of cadaveric shoulders was randomly selected for a modified Weaver-Dunn reconstruction on 1 side and the contralateral side was used for free-tissue graft reconstruction of the coracoclavicular and acromioclavicular ligamentous complexes. Anterior-posterior and superior-inferior acromioclavicular joint translation (in millimeters) was measured with acromioclavicular joint compressions of 10, 20, and 30 N, and with translational loads of 10 and 15 N both before and after acromioclavicular joint reconstruction. Load-to-failure testing was then performed for each construct. Repeated-measures analysis of variance (translational testing) and Wilcoxon signed rank test (load-to-failure testing), both with P = .05, were used for statistical analysis. Results: Mean anterior-posterior and superior-inferior translation of the intramedullary acromioclavicular joint reconstruction was significantly less than that of the modified Weaver-Dunn under all loading conditions (P < .001 and P = .001, respectively), but was not significantly different from that of the intact state (P = .656 and P = .173, respectively). Although the mean ultimate and yield loads and linear stiffness for the intramedullary acromioclavicular reconstruction were greater than that of the modified Weaver-Dunn reconstruction, this did not reach statistical significance (P = .625, P = .625, and P = .625, respectively). Conclusion: Acromioclavicular joint reconstruction with free-tissue graft for both the coracoclavicular and acromioclavicular ligamentous complexes demonstrates initial stability significantly better than a modified Weaver-Dunn and similar to that of intact specimens. Clinical Relevance: This acromioclavicular joint reconstruction provides the surgeon with a relatively nondestructive option.

Biomechanical evaluation of a single-row versus double-row repair for complete subscapularis tears

The purpose of the study was to compare a single-row repair and a double-row repair technique for the specific characteristics of a complete subscapularis lesion. Ten pairs of human cadaveric shoulder human shoulder specimens were tested for stiffness and ultimate tensile strength of the intact tendons in a load to failure protocol. After a complete subscapularis tear was provoked, the specimens were assigned to two treatment groups: single-row repair (1) and a double-row repair using a "suture bridge" technique (2). After repair cyclic loading a subsequent load to failure protocol was performed to determine the ultimate tensile load, the stiffness and the elongation behaviour of the reconstructions. The intact subscapularis tendons had a mean stiffness of 115 N/mm and a mean ultimate load of 720 N. The predominant failure mode of the intact tendons was a tear at the humeral insertion site (65%). The double-row technique restored 48% of the ultimate load of the intact tendons (332 N), while the single-row technique revealed a significantly lower ultimate load of 244 N (P = 0.001). In terms of the stiffness, the double-row technique showed a mean stiffness of 81 N/mm which is significantly higher compared to the stiffness of the single-row repairs of 55 N/mm (P = 0.001). The double-row technique has been shown to be stronger and stiffer when compared to a conventional single-row repair. Therefore, this technique is recommended from a biomechanical point of view irrespectively if performed by an open or arthroscopic approach.

Tensile Strength of Superior Labral Repairs in the Throwing Position

Background Type II superior labral (SLAP) tears commonly occur in athletes in the abducted and externally rotated position in the late cocking phase of throwing. This study investigates arthroscopic repairs of SLAP lesions using a knotless polymeric (KINSA) anchor. Methods Superficial tissues were dissected from 10 cadaveric shoulders. The glenohumeral capsule was preserved. Type II SLAP tears were created through arthroscopic portals and repaired with two anchors anterior and posterior to the biceps tendon. Glenohumeral joints were then fixed in 60° gleno-humeral abduction in the scapular plane with 1 Nm torque in external rotation to recreate the late cocking phase of the throwing cycle. Specimens were mounted onto an Instron machine and the biceps tendon was loaded until failure. Results The mean ultimate peak load was 239 N (SD 101 N). The primary mode of failure was in the tendon substance and 19 out of 20 anchors remained intact in bone. Conclusion To our knowledge this is the first study to investigate arthroscopic SLAP repairs in an intact joint in this susceptible position. We conclude that the KINSA anchor can withstand high tensile loads and may be used to treat SLAP tears in high-demand overhead throwing athletes.

Polyaxial Locking Plate Fixation in Distal Femur Fractures: A Biomechanical Comparison

Uniaxial, first-generation locking plates have become increasingly popular for fixation of supracondylar femur fractures. Polyaxial plates are currently available, which allow for variable-angle screw insertion; however, the biomechanical integrity of these new locking constructs is yet unproven. This study compares the mechanical stability of a conventional locking plate with that of a new polyaxial design. A comminuted supracondylar femur fracture (AO/OTA33-A3) gap model was created in fourth-generation synthetic composite bones. Fixation was obtained with 2 different plate constructs: (1) a conventional locking plate (uniaxial screw heads threading directly into plate) and (2) a polyaxial locking plate (screw heads are captured and "locked" into a fixed angle using locking caps). Eight specimens of each type were then tested in axial, torsional, and cyclic axial modes on a material testing machine. The mean axial stiffness for the polyaxial locking plate was 24.4% greater than the conventional locking plate (168.2 vs 127.1 N/mm; P < 0.0001). The mean torsional stiffness was also greater for the polyaxial plate (2.78 vs 2.57 Nm/degree; P = 0.0226). Cyclic axial loading caused significantly less (P = 0.0034) mean irreversible deformation in the polyaxial plate (5.6 mm) than in the conventional plate (8.8 mm). The mean ultimate load to failure was significantly higher (P = 0.0005) for the polyaxial plate (1560 N) than for the conventional plate (1337 N). The tested plate construct with its polyaxial locking screw mechanism provides a biomechanically sound fixation option for supracondylar femur fractures. The frictional locking mechanism allows maintenance of angular stability while affording the option of variable screw placement.

A biomechanical comparison of six different double loop configurations for use in the lateral fabella suture technique

Six different double loop configurations which could be applied to the lateral fabella suture (LFS) technique were subjected to in vitro mechanical testing. Three double loop, single strand and three double loop, double strand configurations were tested. The strongest configuration, with a significantly higher mean ultimate load and load at yield, was the interlocking loop configuration. This is a novel configuration which has not previously been reported. The three double loop, single strand configurations all had higher mean ultimate loads than the double loop, double strand configurations. The double strand group with uneven loop length performed very poorly, with significantly lower mean stiffness and ultimate load than all of the single strand groups. This group also developed unacceptably high levels of elongation during high level cyclic loading.

A Novel Double-row Rotator Cuff Repair Exceeds Strengths of Conventional Repairs

Double-row rotator cuff repairs are becoming popular because of their ability to improve initial ultimate failure load for full-thickness rotator cuff tears, especially in middle-aged to elderly patients. We hypothesized a quasi-double-row repair using a combination of transosseous sutures, anchors, and double knots (TOAK technique) would exceed the clinically relevant 250-N load threshold and the initial mean ultimate failure loads of anchor-only and transosseous suture-only fixation. In simulated full-thickness supraspinatus tears in cadavers (mean age, 62 years; range, 50-77 years), failure loads of two repair techniques were compared with a TOAK repair using sutures and bioabsorbable anchors. Radiographic densitometry was conducted on all humeral heads. Testing was performed at 6 mm per minute in 18 bones in the following three groups (n = 6 per group): (1) transosseous suture-only with weave-type stitch and single-knot fixation; (2) anchor-only with horizontal mattress stitch and single-knot fixation; and (3) TOAK. The mean ultimate failure load was 238 N for the transosseous suture-only group and 215 N for the anchor-only group. Although the bones had lower density, TOAK specimens failed at 55% to 67% higher loads (mean, 404 N) than the other groups. These data support further evaluation of the TOAK technique for full-thickness supraspinatus tears in middle-aged to elderly patients.

The Mechanical Properties of the Ligamentum Teres

The anatomic and histological characteristics of the ligamentum teres and its vascular contributions to the femoral head have been well described. The function of the ligamentum teres remains poorly understood. Although excision is the current standard in treating complete developmental hip dysplasia, we developed an interest in maintaining, shortening, and reattaching the ligament to assure early postoperative stability in developmental hip dysplasia. To analyze its potential for providing hip joint stability, we investigated the biomechanical properties of the ligamentum teres in an in vitro porcine model. Six immature porcine hips were dissected, with the proximal femur and acetabular anatomy kept intact, isolating the ligamentum teres. Specimens were loaded in tension using custom fixation rigs at 0.5 mm/s in line with the fibers. Data for displacement and force were collected and sampled at 10 Hz for duration of each test. The ligamentum teres failed in a stepwise fashion. The mean ultimate load to failure was 882 +/- 168 N. Mean stiffness and failure stress were calculated as 86 +/- 25 N/mm and 10 +/- 2 MPa, respectively. The biomechanical function of the ligamentum teres is not inconsequential. We found the ultimate load of the ligamentum teres in the porcine model to be similar to those reported for the human anterior cruciate ligament. The strength of the ligamentum teres may confirm its potential for providing early stability in childhood hip reconstructions. In the setting of dysplasia, the preservation and the transfer of the ligamentum teres to augment stability should be considered as an adjunct to open reduction.

Part II: Biomechanical assessment for a footprint-restoring transosseous-equivalent rotator cuff repair technique compared with a double-row repair technique

We hypothesized that a transosseous-equivalent repair would demonstrate improved tensile strength and gap formation between the tendon and tuberosity when compared with a double-row technique. In 6 fresh-frozen human shoulders, a transosseous-equivalent rotator cuff repair was performed: a suture limb from each of two medial anchors was bridged over the tendon and fixed laterally with an interference screw. In 6 contralateral matched-pair specimens, a double-row repair was performed. For all repairs, a materials testing machine was used to load each repair cyclically from 10 N to 180 N for 30 cycles; each repair underwent tensile testing to measure failure loads at a deformation rate of 1 mm/sec. Gap formation between the tendon edge and insertion was measured with a video digitizing system. The mean ultimate load to failure was significantly greater for the transosseous-equivalent technique (443.0 +/- 87.8 N) compared with the double-row technique (299.2 +/- 52.5 N) (P = .043). Gap formation during cyclic loading was not significantly different between the transosseous-equivalent and double-row techniques, with mean values of 3.74 +/- 1.51 mm and 3.79 +/- 0.68 mm, respectively (P = .95). Stiffness for all cycles was not statistically different between the two constructs (P > .40). The transosseous-equivalent rotator cuff repair technique improves ultimate failure loads when compared with a double-row technique. Gap formation is similar for both techniques. A transosseous-equivalent repair helps restore footprint dimensions and provides a stronger repair than the double-row technique, which may help optimize healing biology.

TRANSOSSEOUS EQUIVALENT ARTHROSCOPIC ROTATOR CUFF REPAIR USING PUSH LOCK VERSUS CONVENTIONAL DOUBLE-ROW FIXATION.

Background The newly developed “transosseous-equivalent” (TOSE) rotator cuff repair technique is thought to incorporate several potential biologic and biomechanical advantages to rotator cuff healing. A previous study has shown that the TOSE fixation strength is equivalent to or greater than the conventional double-row (DR) technique; however, arthroscopic lateral fixation using the TOSE method is tedious and technically challenging. Hypothesis The TOSE rotator cuff repair technique employing a knotless suture-locking device for lateral fixation will demonstrate superior loading biomechanics between tendon and tuberosity compared with the conventional double-row technique. Methods Six matched-pairs of fresh-frozen cadaveric shoulders without gross evidence of rotator cuff pathology were used for this study. One specimen of each matched-pair underwent a supraspinatus tendon repair using the TOSE technique; the sutures were secured laterally using the PushLock device (Arthrex, Inc.). The contralateral limb underwent a conventional DR repair. All repairs were performed by the same surgeon. An Instron materials testing machine was used to test the biomechanics of the repair. Each specimen underwent a preload (10 N) followed by a cyclic load (10-180 N - 30 cycles) and a load to failure. Ultimate and yield strength, energy absorption, hysteresis, and linear stiffness data were collected. Results The mean ultimate load to failure for the TOSE technique (380.8 ± 13.2 N) was significantly greater than that of the DR repair (285.5 ± 17.6 N, p = .0015). Energy absorbed to failure was also significantly greater for the TOSE repair (3,966.7 ± 297.4 Nmm) compared with the DR (1,236.2 ± 95.0 Nmm, p = .04). No statistical difference was found for yield strength, initial and linear stiffness, and hysteresis. Conclusions The TOSE repair technique using the PushLock device for lateral fixation demonstrates improved ultimate strength and energy absorption characteristics compared with the conventional DR repair. Clinical Relevance The TOSE rotator cuff repair technique has potential advantages for rotator cuff repair healing, including maximizing footprint-tendon contact, imparting compression on the tendon-bone interface, and generating a stronger repair. The original description and analysis of this technique included the use of a Bio-Tenodesis screw for lateral fixation. In comparison, the PushLock device is much easier and quicker to employ, while maintaining superior loading biomechanical strength. This study validates the use of the PushLock for lateral fixation in the TOSE rotator cuff repair technique.

Effect of thread pitch on pull‐out strength of laparoscopic myoma screws

The purpose of this study was to evaluate the effect of thread-pitch on pull-out strength and bending strength of buttress-thread screws designed for laparoscopic myoma extraction. The ultimate failure load of four 5-mm diameter buttress-thread screws with 3-, 4-, 5-, and 6-mm thread pitch, 40 mm in thread-length were examined on fresh myoma specimens. The myoma tissue at each traction site was evaluated histologically to determine its density. The critical minimal pull-out strength based on moderate-density myoma group was estimated. The bending strength was also determined for each screw. A wide range of ultimate failure loads with a mean +/- SE of 129.3 +/- 5.5 N (range, 30.4-255.7 N) for all screws and tissue densities was recorded. In moderate-density myomas, the mean ultimate failure loads decreased linearly with increasing thread-pitch from 3 mm (148.0 +/- 9.5 N) to 6 mm (119.8 +/- 9.4 N) (test for trend: P < 0.05). Based on the criterion of a minimum pull-out strength of at least 50 N in not less than 95% of tractions in medium-density myomas, the 3-mm and 5-mm pitch screws were found to have acceptable properties. The 5-mm pitch screw had less thread-turn than the 3-mm pitch for the same thread-length and would need less application time. The bending strength also decreased with increasing thread pitch from 3 to 5 mm, then became stable at around 15 N. The pull-out strength of soft tissue buttress-thread screws decreased linearly with increasing thread-pitch. Thread-pitch should be considered when designing laparoscopic myoma-screws.

Mechanical Evaluation of Two Crimp Clamp Systems for Extracapsular Stabilization of the Cranial Cruciate Ligament‐Deficient Canine Stifle

To compare the mechanical properties and interoperator variabilities of 2 crimp clamp systems for extracapsular, fabello-tibial, nylon loop stabilization of the cranial cruciate ligament-deficient stifle in dogs. In vitro mechanical testing. Three operators with different grip strengths each secured 20 standardized nylon loops using stainless-steel crimp clamps: 10 using a Veterinary Instrumentation system (45 kg [100 lb] test nylon leader line, 12 mm crimp clamps) and 10 using a Securos system (36 kg [80 lb] test nylon leader line, 36 kg [80 lb] crimp clamps). Loops were tensile loaded to failure in a materials testing machine. Mean ultimate load and mean stiffness were significantly higher for the Securos (336.9 N, 60.6 N/mm) than for the Veterinary Instrumentation system (113.8 N, 37.0 N/mm). For both systems, ultimate load was subject to interoperator variability. The Securos loops were significantly stronger and stiffer than the Veterinary Instrumentation loops for all operators, but significant differences between operators for ultimate load existed for both systems. Securos fabello-tibial sutures will withstand greater loads than Veterinary Instrumentation sutures and this is particularly true for sutures created by surgeons with reduced grip strength. It may be necessary to use more than 1 Veterinary Instrumentation suture to match the ultimate load and stiffness of a Securos suture.

Mechanical Evaluation of Two Loop Tensioning Methods for Crimp Clamp Extracapsular Stabilization of the Cranial Cruciate Ligament‐Deficient Canine Stifle

To describe a method of tightening nylon loops secured with a crimping system for extracapsular fabello-tibial stabilization of the cranial cruciate ligament-deficient stifle and to compare this with a method using a commercially available tensioning device. In vitro mechanical testing. Fourteen standardized nylon loops were tensioned using a tensioning device and secured with crimp clamps. Another 14 loops were tightened by partially securing the crimp clamp, followed by tightening of the loop by hand, before definitively securing the crimp clamp. Loops were loaded to failure in a materials testing machine. Mean ultimate loads for instrument-tightened and hand-tightened loops were 383.7 and 371.4 N, respectively. Mean stiffness values for instrument-tightened and hand-tightened loops were 59.7 and 59.3 N/mm, respectively. These differences were not significant. The hand tightening method does not affect the mechanical properties of the loop. The hand tightening method described is a valuable technique for unassisted surgeons without access to tensioning devices.

Biomechanical Evaluation of the Relation Between Number of Suture Anchors and Strength of the Bone–Tendon Interface in a Goat Rotator Cuff Model

The effect of contact area between tendon and bone on ultimate pullout strength of a repaired tendon is not known. The purpose of this study was to test whether the strength of a healed bone-tendon interface is related to the amount of tendon that is in contact with bone at the time of repair. A total of 20 mature goats underwent bilateral open rotator cuff repair of the infraspinatus tendon. The tendon edge was repaired to bleeding cancellous bone in each case with the use of suture anchors. The tendon was repaired with 2 anchors (contact area A; n = 20) on 1 shoulder and 4 anchors (contact area B; n = 20) on the contralateral shoulder. Ten goats were euthanized at 4 weeks (group 1) and 10 goats at 8 weeks (group 2) postoperatively. Twelve specimens were evaluated with ultrasound in the sagittal and coronal planes in a saline bath before mechanical testing was conducted. Ultimate load to failure was reported for each shoulder. Data were analyzed by means of a paired t test and Wilcoxon signed-rank test. Ultrasound evaluation revealed several instances in groups 1/2 and contact areas A/B in which clear gap formation occurred without scar (collagen) interdigitation at the bone-tendon interface. Failures occurred at the bone-tendon repair site in all specimens during biomechanical testing. The mean load to failure for all specimens in group 1 was 350.7 N; it was 619.4 N for specimens in group 2 (P = .0002). In group 1, specimens with contact area A had a mean load to failure of 317.3 N; specimens with contact area B had a mean load to failure of 375.5 N (P = .15). In group 2, specimens repaired with contact area A had a mean ultimate load to failure of 635.8 N, whereas contact area B specimens had an ultimate failure strength of 688.5 N (P = .45; Wilcoxon signed-rank). Increasing the number of suture anchors and the surface area of the tendon that is in contact with bone at the repair site increased the ultimate load to failure of the repaired tendon at both 4 and 8 weeks postoperatively by less than 10% at both intervals. This was not a statistically significant increase in failure strength in this model. This animal model shows no statistically significant differences in strength at the repair site between a 2-anchor and a 4-anchor rotator cuff repair. This information may have direct clinical applications for the surgical technique employed in the repair of rotator cuffs.

The Biomechanical Evaluation of Four Fixation Techniques for Proximal Biceps Tenodesis

The purpose of this study was to compare the cyclic displacement and ultimate failure strength of 4 proximal biceps tendon tenodesis fixation methods: the open subpectoral bone tunnel (SBT) biceps tenodesis, the arthroscopic suture anchor (SA) tenodesis, the open subpectoral interference screw (SIS) fixation technique, and the arthroscopic interference screw (AIS) technique. Biomechanical experimental control. Twenty fresh-frozen cadaver shoulders were dissected free of soft tissues, leaving the proximal humerus and the proximal biceps tendon as a free graft. Specimens were randomized to 1 of 4 groups with 5 total specimens in each group. A proximal biceps tenodesis was performed according to the techniques listed above. The specimens were mounted for an axial pull of the biceps tendon on a servohydraulic materials testing system with a 100-N load cycled at 1 Hz for 5,000 cycles, followed by an axial load to failure test. Cyclic displacement, ultimate load to failure, and site of failure were recorded for each specimen. The mean cyclic displacement recorded for each experimental group was as follows: SBT group, 9.39 +/- 2.82 mm; AIS group, 5.26 +/- 2.60 mm; SIS group, 1.53 +/- 0.60 mm; and SA group, 3.87 +/- 2.11 mm. The mean ultimate failure loads after 5,000 cycles were as follows: SBT group, 242.4 +/- 51.33 N; AIS group, 237.6 +/- 27.58 N; SIS group, 252.4 +/- 68.63 N; and SA group, 164.8 +/- 37.47 N. Each specimen failed at the tenodesis site. The SBT group showed statistically significant greater displacement than the other tenodesis methods. There were no statistically significant differences in ultimate failure strength between any of the biceps tenodesis methods tested. The data serve as a guide to the surgeon performing a proximal biceps tenodesis in choosing a fixation method.

Biomechanical testing of quadriceps tendon–patellar bone grafts: an alternative graft source for press-fit anterior cruciate ligament reconstruction?

Press-fit fixation of bone-patellar tendon-bone (BPTB) grafts in anterior cruciate ligament (ACL) reconstruction has been analyzed biomechanically in previous studies; however, the use of quadriceps tendon-patellar bone (QTPB) grafts has not been studied so far. It is hypothesized that QTPB grafts provide primary fixation strength comparable to BPTB grafts in press-fit ACL reconstruction with respect to bone plug length and loading angle. Fifty-two QTPB grafts were harvested from fresh human cadaver knees (mean age 73.3 years) with the length of the patellar bone plug being either 15 mm (Group I) or 25 mm (Group II). The grafts were anchored within fresh porcine femora (mean age 12 months) using a press-fit fixation technique. Forty-eight specimens were loaded to failure at 10 mm/s with varying loading angles of 0 degrees , 30 degrees , and 60 degrees until failure. A microradiographic pre-post-implantation analysis was conducted on four grafts. The biomechanical testing showed a significant difference in the ultimate failure loads comparing Group I (mean 224+/-79.3 N) to Group II (mean 339+/-61.4 N), both showing mean ultimate failure loads to increase with rising loading angle. The predominant mode of failure was graft pullout at axial loading and tendon rupture at 60 degrees loading angle. The microradiographic analysis revealed an iatrogenic damage of the bone-tendon junction on the cancellous aspect of the bone plug in all trials, corresponding with the site of impactor placement during implantation. QTPB grafts provide a loading capability comparable to BPTB grafts in press-fit ACL reconstruction. The broad and profound area of quadriceps tendon attachment to the patellar bone plug makes graft implantation demanding.

Fixation of the graft in reconstruction of the anterior cruciate ligament

Methods of reconstruction of the anterior cruciate ligament (ACL) have developed considerably over the last 15 years. Primary repair and extra-articular procedures have failed to reproduce satisfactory stability of the knee[1][1] and the use of prosthetic ligaments has been abandoned.[2][2] These

STRUCTURAL PROPERTIES OF THE SUPRASPINATUS TENDON IN TWO JOINT POSITIONS

The supraspinatus tendon is frequently involved in rotator cuff tears. It has been suggested that joint position affects the structural mechanics of the tendon–bone complex. The purpose of this study was to determine regional variations in structural properties of the supraspinatus tendon in two glenohumeral positions. Supraspinatus tendons from 17 fresh frozen cadavers were divided into three strips of equal width and tested with a material-testing machine. The arm orientation was either in hanging position or 60 degrees glenohumeral abduction corresponding to 90 degrees arm abduction assuming 30 degrees scapular rotation. Tensile force, tendon elongation and failure mode were recorded. Overall, there was no significant difference in structural properties between hanging arm position and 60 degrees of glenohumeral abduction (p&gt;0.05). However, the mean ultimate load (385 N, SD 56 N) and mean ultimate stress (14 MPa, SD 3 MPa) of the anterior tendon section with the arm in glenohumeral abduction were lower in 60 degrees abduction than in the hanging arm position (611 N, SD 276 N; 24 MPa, SD 10 MPa). In hanging arm position, the anterior tendon portion had a significantly greater ultimate load and stiffness than the middle and posterior portions (p&lt;0.05). The regional variation in structural properties substantiates the clinical finding that rotator cuff ruptures easily extend posteriorly. Our study suggests that glenohumeral abduction reduces the failure strength of the supraspinatus tendon, specifically of its anterior portion. In our study, the maximum load of the anterior portion was substantially higher than predicted maximum loads transmitted physiologically through the entire tendon.

Structural Properties of the Supraspinatus Tendon in Two Joint Positions

The supraspinatus tendon is frequently involved in rotator cuff tears. It has been suggested that joint position affects the structural mechanics of the tendon–bone complex. The purpose of this study was to determine regional variations in structural properties of the supraspinatus tendon in two glenohumeral positions. Supraspinatus tendons from 17 fresh frozen cadavers were divided into three strips of equal width and tested with a material-testing machine. The arm orientation was either in hanging position or 60 degrees glenohumeral abduction corresponding to 90 degrees arm abduction assuming 30 degrees scapular rotation. Tensile force, tendon elongation and failure mode were recorded. Overall, there was no significant difference in structural properties between hanging arm position and 60 degrees of glenohumeral abduction (p>0.05). However, the mean ultimate load (385 N, SD 56 N) and mean ultimate stress (14 MPa, SD 3 MPa) of the anterior tendon section with the arm in glenohumeral abduction were lower in 60 degrees abduction than in the hanging arm position (611 N, SD 276 N; 24 MPa, SD 10 MPa). In hanging arm position, the anterior tendon portion had a significantly greater ultimate load and stiffness than the middle and posterior portions (p<0.05). The regional variation in structural properties substantiates the clinical finding that rotator cuff ruptures easily extend posteriorly. Our study suggests that glenohumeral abduction reduces the failure strength of the supraspinatus tendon, specifically of its anterior portion. In our study, the maximum load of the anterior portion was substantially higher than predicted maximum loads transmitted physiologically through the entire tendon.

Biomechanical properties of braided polyester tapes intended for use as intra-articular cranial cruciate ligament prostheses in dogs.

To determine the in vitro structural and material properties of braided, multifilament, nonabsorbable polyester tapes, used for intra-articular stabilization of cranial cruciate ligament- (CCL-) deficient stifle joints in dogs, and compare those with properties of multifilament polyamide tapes. 30 polyester tapes (width, 4 mm), 10 polyester tapes (width, 7 mm), and 30 polyamide tapes (width, 4 mm) were tested to failure. Cyclic loading experiments were also performed, using 3 polyester tapes of each width. Tapes were mounted in a tensile tester as single loops, simulating intra-operative conditions, and elongated to failure at 1,000 mm/min. Additionally, the behavior of polyester tapes was tested at different elongation rates. In a second series of experiments, biomechanical variables of the polyester tapes were measured after 25 sets of 2,000 cycles between physiologic force limits. Mean (+/- SD) ultimate loads of the 4-mm wide polyamide tapes, 4-mm wide polyester tapes, and 7-mm wide polyester tapes were 266.48 +/- 13.19 301.78 +/- 16.92, and 726.40 +/- 37.74 N, respectively. Corresponding stiffnesses were 15.57 +/- 0.49, 21.63 +/- 2.19, and 34.85 +/- 2.66 N/mm, respectively. Failure properties of polyester tapes were affected by previous cyclic loading. Polyester tapes of 4- or 7-mm widths should be able to resist forces resulting from weight bearing in dogs, suggesting that these tapes will be effective for stabilization of the stifle joint in dogs with a ruptured CCL.